The present application relates primarily to a hydraulic hybrid powertrain for a vehicle and to various methods of operating said hydraulic hybrid powertrain.
A hybrid vehicle may be equipped with a secondary energy storage system on board, in addition to a fuel tank. The secondary energy storage system enables additional degrees of freedom in the generation of tractive power and adds the ability to regenerate energy during braking, allowing the subsequent reuse of the stored energy. As a result, fuel consumption may be reduced or vehicle performance may be increased. In an electric hybrid system, energy is stored in electrochemical batteries or supercapacitors, and a secondary machine is an electric motor.
Several hybrid architectures and technologies exist, suited to different applications: among these, series, parallel, and power-split architectures are the most common.
A parallel hybrid powertrain is characterized by a mechanical coupling of the engine and the secondary machine, which allows both to provide torque to a ground engaging portion of the powertrain. Based on the location of a torque summation node, the following categories of parallel hybrid architecture are normally distinguished: a pre-transmission parallel hybrid architecture, where a secondary machine, powered by an alternative source of energy, is placed between an engine and a transmission; and a post-transmission parallel hybrid architecture, where a secondary machine, powered by an alternative source of energy, is placed between a transmission and a ground engaging portion of the powertrain.
Additionally, a third solution is possible which includes placing an electric motor at an intermediate position in the transmission, as described in U.S. Pat. No. 8,353,804 B2 and as shown in FIG. 1, which introduces a hybrid transmission where both an electric motor and an engine are connected to an off-highway, power shifting transmission. The electric motor is mechanically connected to the transmission between the forward/reverse direction clutches and the range clutches; the motor is electrically powered by supercapacitors.
The configuration described in U.S. Pat. No. 8,353,804 B2 and as shown in FIG. 1 allows optimizing the efficiency of the hybrid transmission, since the electric motor power goes through one less conversion before reaching a transmission output (when compared to a pre-transmission parallel hybrid architecture). Further, the solution offers a torque multiplication factor of the range gears, which enables the use of a smaller motor in comparison to a post-transmission parallel hybrid architecture.
However, notwithstanding the above-described developments, there continues to exist a strong demand for long-lived, high-efficiency hybrid powertrains capable of providing high output torques.